Large size real-time 3-D display with wide viewing angle has long been dreamed of. We may classify existing 3-D display techniques roughly into two classes, pseudo 3-D display and true 3-D display. In pseudo 3D-display various means are employed to present respectively to two eyes of an observer two pictures being taken at slightly different angles. The observer combines the two pictures and forms a virtual 3-D image in his/her mind. In true 3-D display a real 3-D image is created in space, like what happens in holographic display. To watch pseudo 3-D display one has to wear some kind of auxiliary apparatuses like polarization spectacles, or the eye position of an observer has to be tracked, limiting the number of observers to one or a few more. For true 3-D display observers need not wear any auxiliary apparatus and could watch a displayed 3-D image conveniently as if they watch a real object.
For the past decades with the development of liquid crystal display (LCD), people tried to replace hologram plates with liquid crystal panels and succeed in real-time holographic 3-D display for very small objects. However even for projection type liquid crystal panels the pixel pitch is usually more than ten micrometers, in other words the space resolution is less than one hundred line pairs per millimeter, which is nearly two orders lower than that of a hologram plate. Therefore the holographic 3-D images generated so far by using projection type liquid crystal panels were as small as one centimeter so that very low density interference patterns were involved. At the same time the created holographic 3-D images were far away from the liquid crystal panels, yielding a very narrow viewing angle.
For conventional liquid crystal computer screens the pixel pitches increase to about 0.29 mm, which means the resolutions are only several line pairs per millimeter. It is impossible to generate 3-D holographic images with such low resolution liquid crystal screens. In addition to produce a large size holographic 3-D image with wide viewing angle large space-bandwidth product is necessary. At present, liquid crystal panels could only provide a space-bandwidth product around 106, several orders lower than what is necessary. To make things worse with the increase of space-bandwidth product huge data becomes inevitable, which puts a great burden on real time data processing.